A transient molecular probe for characterizing the surface properties of TiO2 nanoparticle in colloidal solution

A transient molecular probe for characterization of the surface properties of TiO2 nanoparticles in colloidal solution has been developed recently in our laboratory. The probe molecule is all-trans-retinoic acid (ATRA) adsorbed on the TiO2 nanoparticle surface. After photoexcitation, the photoinduced interfacial charge recombination would generate ATRA triplet state (ATRA T) with a substantial quantum yield. While the quantum yield of triplet ATRA generated in the solution phase is substantially low, which renders the interfacial-charge-recombination generated triplet ATRA being a transient probe molecule specific only to the interface. It is found that the triplet-triplet absorption spectrum of ATRA adsorbed molecule is sensitive to its binding form with the surface Ti atom through the carboxylic group, as well as to the polarity of the medium. Especially the apparent lifetime of ATRA(T) at the TiO2 surface changes substantially when the local polarity around the TiO2 nanoparticle changes. We found that the ATRAT monolayer adsorbed at the TiO2 surface can be used as a transient molecular probe for the surface binding forms, coordination state of the surface Ti atoms and the light-induced wettability change of the TiO2 nanoparticle. TiO2 nanoparticle, all-trans-retinoic acid, molecular probe, interfacial charge recombination, surface binding form, light-induced wettability change.